The full blown screeching noise is:
* A loose belt
* Failing alternator (drag)
* You got grease / oil on the V-face of the belts and they are slipping.

If it is a greased belt, a cheap bar of LYE (or any) soap eliminates the horrid sound.

Going out on a limb for this one; The sound from the first video is:

#1. The alternator and/or pulley
#2. The harmonic balancer pulley mounting screws are failing (allowing the pulley to rock / shift).
#3. The harmonic balancer is damaged, rocking / shifting on the crankshaft.

.

__________________
ASE Master Mechanic

Prototype R&D/testing:
Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician.
Noise Vibration and Harshness (NVH).
Dynamometer.
Heat exchanger durability.
HV-A/C Climate Control.
Vehicle build.
Fleet Durability
Technical Quality Auditor.
Automotive Technical Writer

1985 300SD
1983 300D

https://www.boldegoist.com/